This invention relates generally to dry powder toner xerography, and more particularly to a low toner pile height color electrostatographic reproduction machine for producing high quality color toner images approximating the xe2x80x9clook and feelxe2x80x9d of lithographically produced color images. In an electrostatographic printing machine, a photoconductive member is charged to a substantially uniform potential to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to a light image of a document being reproduced. Exposure of the charged photoconductive member selectively dissipates the charge thereon in irradiated areas. This records an electrostatic latent image on the photoconductive member corresponding to the informational areas contained within the document being reproduced.
After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing developer material containing charged toner particles, for example, black toner particles, into contact therewith. Developer material can be single component comprising only of charged toner particles, or it may be dual component comprising carrier particles and toner particles that are triboelectrically charged when admixed or mixed with the carrier particles. In either case, bringing the developer material into contact with the latent image forms a toner image on the photoconductive member which is subsequently transferred to a copy sheet. The copy sheet is then separated from the photoconductive member and the toner powder is fed on the copy sheet through a fusing apparatus where it is heated to permanently affix it to the copy sheet, thus forming a black and white copy or print of the document.
Multi-color electrostatographic printing machines which use multi-colored toners are substantially identical in each color image forming process to the foregoing process of black and white printing which uses only black toner. However, rather than forming a single latent image on the photoconductive surface, several single color latent images corresponding to color separated light images of the original document are recorded thereon. Each single color electrostatic latent image is developed with toner particles of a color complementary thereto. This process may be performed in a single pass, or in multipasses during which image formation is repeated a plurality of cycles for differently colored images using their respective complementarily colored toner particles to form color toner images. Each single color toner powder image is transferred to a copy sheet in superimposed registration with the other toner powder images.
This creates a composite multi-layered toner powder image on the copy sheet. The copy sheet is separated from the photoconductive member and, thereafter, the multi-layered toner powder image on the sheet is fed through a fusing apparatus and permanently affixed to the copy sheet, thus creating a multi-color document. In a black and white or multi-color electrostatographic printing machine, the copy sheet is typically brought into moving contact with the photoconductive member during toner powder image transfer to the copy sheet. A sheet transport apparatus is typically provided for receiving the copy sheet incrementally as it is incrementally separated from the photoconductive member, and for transporting the copy sheet towards and into the fusing apparatus.
High toner pile height is a major document appearance problem for dry powder Xerography. High toner pile height is obvious or noticeable to customers, not only as increased document thickness but also in other undesirable ways, such as paper curl. The problem is compounded by the fact that toner pile height also varies within a page from zero in white areas to a maximum value in very dark toned areas. This leads to further document appearance degradation in terms of ripple (non-uniform curl), and differential gloss, for examples. Such paper distortion problems or defects are important in high quality dry or powder toner applications which are intended to compete in a market that is accustomed to the document xe2x80x9clook and feelxe2x80x9d of lithography. Similarly, these issues will become even more important for applications which require the apparently more demanding xe2x80x9clook and feelxe2x80x9d of photography.
In addition to being aesthetic dissatisfiers, paper distortion problems or defects due to curl and ripple undesirably also increase the jam rate of paper handling in the machine, and thus complicate paper handling and document finishing. This is objectionable in any market, but especially in the high speed production color printing market.
There is therefore a need for a low toner pile height color electrostatographic reproduction machine that is suitable for producing high quality color toner images approximating or having the xe2x80x9clook and feelxe2x80x9d of lithographically produced color images, if powder toner xerography is to become a serious contender in markets where the xe2x80x9clook and feelxe2x80x9d images is important.
In accordance with the present invention, there is provided a low toner pile height color image reproduction machine for forming full-gamut toner images approximating a xe2x80x9clook and feelxe2x80x9d of offset lithographic images. The reproduction machine includes a single moveable endless image bearing member having a path of movement; at least a charging device mounted along the path of movement for uniformly charging a portion of the image bearing member; a controller including an image processor for converting red, green, blue (RGB) digital image signals into at least seven bitmaps pixels of color separation images including black (K), cyan (C), red (R), magenta (M), blue (B), green (G) and yellow (Y); at least an exposure device mounted along the path of movement for imagewise exposing the portion of the single moving image bearing member to a light pattern of a first one of the at least seven bitmaps to form a first color separation latent image having first image areas and first background areas; and at least a development apparatus mounted along the path of movement for developing the first image areas of the first color separation latent image using toner particles having a color corresponding to that of the first one of the at least seven bitmaps.